The present invention relates to novel borane derivatives, various materials and organic electroluminescent devices (hereinafter referred to as xe2x80x9corganic EL devicexe2x80x9d) comprising the borane derivatives. Specifically, this invention relates to borane derivatives having novel structures, and various materials and organic EL devices comprising the borane derivatives having the structures, which are useful as electronic functional materials and optical functional materials.
Various institutions have tried to apply xcfx80 electron type organic compounds to optical functional materials and electronic functional materials in various ways.
Among them, borane compounds which intramolecularly contain boron atoms have unique optic and electronic properties probably owing to the existence of the empty p orbital of the boron atom. However, the borane compounds have generally been unsuitable for the use as such materials, because of their instability to air and water.
With respect to such a problem, it has been reported that the borane compound can become stable to air and water when constituted so as to be bulky, namely, when introducing bulky substituents around a boron atom so as not to expose the boron atom outward. Thus it is highly likely that the borane compound having such a structure can apply for nonlinear optical materials and organic EL devices.
Examples of borane compounds stable in the air have been reported in J. Chem. Soc. Chem. Commun., 1998, 963 (hereinafter referred to as Document 1), J. Am. Chem. Soc., 120, 10776(1998) (hereinafter referred to as Document 2), and J. Am. Chem. Soc., 120, 5112 (1998) hereinafter referred to as Document 3). Further, applications of borane compounds to nonlinear optical materials have been reported in Appl. Organomet. Chem., 10, 305(1996) (hereinafter referred to as Document 4). In addition, an application of borane compounds to organic EL devices has been reported in J. Am. Chem. Soc., 120, 9714 (1998) (hereinafter referred to as Document 5).
Documents 2 and 3 describe the maximum fluorescent wavelength, but the descriptions are limited to the luminescence property in solution state. There is no description on the luminescence property in solid state which is actually used in such application. Further, the structures disclosed are limited to polymers, and there is no description on any low molecular weight compounds.
Document 4 also describes the fluorescent property in the solution state, but there is neither description about the luminescence in the solid state, nor description about applications for the luminescent materials.
Thus the studies have not been made sufficiently for using the xe2x80x9cbulkyxe2x80x9d borane compound in any substantial applications at present. Particularly, there has been a demand to apply the borane material to the organic EL devices. Many studies have been made in order to find such a compound as the device, which has not led to any satisfactory result yet.
The organic EL device essentially comprises a structure wherein an organic compound as a charge transport material and/or a luminescent material is sandwiched in between two electrodes. The highly efficient organic EL device of a low power consumption is required, and thus it is necessary to select an organic compound of high luminous efficiency as the luminescent material.
Document 5 describes some borane compounds such as 5,5xe2x80x2-bis(dimesitylboryl)-2,2xe2x80x2-(bithiophene) and 5,5xe2x80x3-bis(dimesitylboryl)-2,2xe2x80x2:5xe2x80x2,2xe2x80x3-(terthiophene) used for electron transport materials (charge transport materials), but does not mention their luminescence property or suitability for luminescent materials. This literature merely mentions the device comprising the borane compound having a lower current density, i.e., a more improved luminous efficiency, than that of the device of the same luminance not comprising the borane compound.
JP-A 7-102251 also describes an example of the boron compound used for the organic EL device. However, this boron compound requires a high voltage for driving the device, and has a low luminance.
Since there are few literatures on the luminescence property of borane compounds, any highly efficient organic EL device of a low power consumption has not been prepared by using borane compounds known as a raw material for the organic EL device. Therefore, there has been a demand for a borane compound having a specific structure effective as a material for an organic EL device.
The present inventors have made intensive studies in order to provide a new borane derivative, and various materials and organic EL devices each comprising the borane derivative. As a result, the inventors have found that a borane derivative having a specific structure, and a material, particularly an organic EL device, comprising the borane derivative can solve the above-mentioned problems, whereby the present invention have been achieved.
The present invention is described below in detail.
The borane derivative of the present invention is a new compound represented by the following formula (1). The present borane derivative is expected to be used in a wide variety of applications such as electronic functional materials and optical function materials taking advantage of electronic properties originating from the borane atom, as well as for luminescent materials and charge transport materials. 
wherein R1 to R8 and Z2 are each independently a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, a substituted boryl group, an alkoxy group or an aryloxy group; X, Y and Z1 are each independently a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, an alkoxy group or an aryloxy group; substituents of Z1 and Z2 may be united to form a condensed ring; and n is an integer of 1-3;
with the provisos that when n is two or more, Z1s may be different from each other; and that cases where n is 1, X, Y and R2 are each methyl, and R8 is a hydrogen atom or substituted boryl and those where n is 3 and Z1 is methyl are excluded.
Among the borane derivatives represented by the formula (1), preferable are those wherein at least one substituted or unsubstituted 9-anthryl group is bonded to the boron atom.
Concrete examples of the borane derivative according to this invention include the compounds represented by the following formulae (3) to (9). 
The compound represented by the formula (3) is one of the borane derivatives of the above formula (1) wherein n is 3, R4 to R8 are each hydrogen atom, and Z1 and Z2 are benzo-condensed. 
The compound represented by the formula (4) is one of the borane derivatives of the above formula (1) wherein n is 3, R4 to R7 are each hydrogen atom, one R8 is a dianthrylboryl group and the other two R8s are each hydrogen atom, and Z1 and Z2 are benzo-condensed. 
The compound represented by the formula (5) is one of the borane derivatives of the above formula (1) wherein R4 to R7 are each hydrogen atom, R8 is phenyl, n is 3, and Z1 and Z2 are benzo-condensed. 
The compound represented by the formula (6) is one of the borane derivatives of the above formula (1) wherein n is 2, R1 and R3 to R8 are each hydrogen atom, R2, X and Y are each methyl group, and Z1 and Z2 are benzo-condensed. 
The compound represented by the formula (7) is one of the borane derivatives of the above formula (1) wherein n is 2, R1 and R3 to R7 are each hydrogen atom, R2, X and Y are each methyl group, one R8 is anthrylmesitylboryl, the other R8 is a hydrogen atom, and Z1 and Z2 are benzo-condensed. 
The compound represented by the formula (8) is one of the borane derivatives of the above formula (1) wherein n is 3, R4 to R8 are each hydrogen atom, Z1 and Z2 are benzo-condensed at one position, the other two Z1s not condensed are a methyl group, and the other two Z2s not condensed are a hydrogen atom. 
The compound represented by the formula (9) is one of the borane derivatives of the above formula (1) wherein n is 1, R1 and R3 to R7 are each hydrogen atom, R2, X and Y are each methyl group, R8 is a phenyl group, and Z1 and Z2 are benzo-condensed.
The borane derivative, which is used as various materials according to this invention, namely, luminescent materials, charge transport materials and materials for organic EL devices (luminescent layer, charge transport layer), is represented by the following formula (2): 
wherein R1 to R8 and Z2 are each independently a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, a substituted boryl group, an alkoxy group or an aryloxy group; X, Y and Z1 are each independently a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, an alkoxy group or an aryloxy group; substituents of Z1 and Z2 may be united to form a condensed ring; and n is an integer of 1-3; with the proviso that when n is two or more, Z1s may be different from each other.
The borane derivative preferably has a xe2x80x9cbulkyxe2x80x9d structure so as to be stable even in the air and to show enough durability and performance as such a material. The borane derivative preferably has an anthracene ring and/or a naphthalene ring.
Therefore, the luminescent material, charge transport material and organic EL device of this invention preferably comprise the borane derivatives represented by the formula (2), wherein at least one substituted or unsubstituted 9-anthryl group is bonded to a boron atom.
Concrete examples of such a borane derivative include the compounds represented by the following formulae (10) to (14), in addition to those of the aforementioned formulae (3) to (9). 
The borane derivative according to this invention and the borane derivative used for the materials according to this invention (hereinafter abbreviated as xe2x80x9cthe borane derivative of this inventionxe2x80x9d for convenience) may be synthesized by various known methods including a typical synthesis shown below. Specifically, the borane derivative of this invention can be obtained by the reaction of the compound represented by the following formula (15) with a base, followed by the reaction with a borane compound.
ArWxe2x80x83xe2x80x83(15) 
wherein Ar denotes the following formula (16) or (17), and W is a halogen atom. 
wherein R1 to R3 are each independently a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, a substituted boryl group, an alkoxy group or an aryloxy group; and X and Y are each independently a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, an alkoxy group or an aryloxy group; and 
wherein R4 to R8 and Z2 are each independently a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, a substituted boryl group, an alkoxy group or an aryloxy group; and Z1 is a saturated or unsaturated hydrocarbon group, an aromatic group, a heterocyclic group, a substituted amino group, an alkoxy group or an aryloxy group; or Z1 and Z2 may be united to form a condensed ring.
The base to be used in this method includes, for example, organolithium reagents such as n-butyl lithium, tert-butyl lithium and phenyl lithium, and magnesium reagents such as magnesium and magnesium bromide. The solvent to be used is not particularly limited and any solvent may be used as far as it is inert to the base used. In general, ether solvents such as diethyl ether and tetrahydrofuran (hereinafter abbreviated as xe2x80x9cTHFxe2x80x9d), and aromatic solvents such as benzene and toluene may be used. The borane compound to be used includes halogenated boranes such as trichloro borane, trifluoro borane, and complexes thereof; and alkoxy boranes such as trimethoxy borane and triisopropoxy borane.
The reactions as mentioned above are preferably carried out in an inert gas such as nitrogen and argon gas. The reaction temperature is not particularly limited but usually and preferably in the range of xe2x88x9278xc2x0 C. to 120xc2x0 C. The reaction time is not particularly limited also, and the reaction may be stopped when the reaction sufficiently progressed. The reaction may be confirmed by a conventional analytical means such as NMR and chromatography, and the end of the reaction may be determined at the optimum point in the analysis.
The borane derivatives of this invention may also be obtained by substitution reaction of the compound obtained by above-mentioned method. The substituent to be added to the compound by the substitution may include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, cyclopentyl and tert-butyl; alkenyl groups such as vinyl, allyl, butenyl and styryl; alkoxy or aryloxy groups such as methoxy, ethoxy, propoxy and phenyloxy; amino groups such as dimethylamino and diphenylamino; silyl groups such as trimethylsilyl, dimethyl-tert-butyl silyl, trimethoxysilyl and triphenylsilyl; boryl groups such as dianthrylboryl and dimesitylboryl; aryl groups such as phenyl, naphthyl, anthryl, biphenyl, toluyl, pyrenyl, perylenyl, anisyl, terphenyl and phenanthrenyl; and heterocyclic groups such as hydrofuryl, hydropyrenyl, dioxanyl, thienyl, furyl, oxazolyl, oxadiazolyl, thiazolyl, thiadiazolyl, acridinyl, quinolyl, quinoxalinyl, phenanthrolinyl, benzothienyl, benzothiazolyl, indolyl, silacyclopentadienyl and pyridyl.
In addition, these substituents may form a ring structure by bonding to each other at any site in the compound.
The organic EL device according to this invention essentially has a structure wherein a borane derivative layer comprising the borane derivative represented by the formula (2) as a main component is sandwiched in between a pair of electrodes (anode and cathode).
The borane derivative is suitable as a material for both a luminescent layer and a charge transport layer (hole injection layer, hole transport layer, electron injection layer and electron transport layer), because it can be used as both a luminescent material and an electron injection material. The borane derivative layer thus obtained effectively acts as a luminescent layer and a charge transport layer.
The borane derivative layer may further comprise any of hole injection materials, hole transport materials, luminescent materials, electron injection materials and electron transport materials in addition to the borone derivative of this invention.
The organic EL device may comprise an electron-donating compound and an electron-accepting compound, which are added in admixture or laminated, as a charge transport material in many cases. It is known that these compounds form unfavorable charge-transfer complex or exciplex. However, the borane derivatives of this invention has a structure in which xe2x80x9cbulkyxe2x80x9d substituents bonded to a boron atom are propeller-like located around the boron atom, and therefore, it is difficult to form the charge-transfer complex or exciplex in this compound. Accordingly, the highly efficient element can advantageously be obtained, when using borane derivatives for the organic EL device as the electron-donating compound or electron-accepting compound.
The organic EL device according to this invention may optionally comprise any additional layers such as hole injection layers, hole transport layers, luminescent layers, electron injection layers, electron transport layers and interlayers, in addition to the borane derivative layer, between the electrodes.
The following are concrete examples of the organic EL device of this invention having laminated structures:
(1) anode/borane derivative layer/cathode;
(2) anode/hole injection layer/borane derivative layer/cathode;
(3) anode/borane derivative layer/electron injection layer/cathode;
(4) anode/hole injection layer/borane derivative layer/electron injection layer/cathode;
(5) anode/hole injection layer/borane derivative layer/electron transport layer/interlayer/cathode;
(6) anode/hole injection layer/hole transport layer/borane derivative layer/electron injection layer/cathode; and
(7) anode/hole injection layer/hole transport layer/borane derivative layer/electron injection layer/interlayer/cathode.
Although hole injection layers, electron injection layers, hole transport layers, electron transport layers and interlayers are not always essential in this invention, they improve the luminous efficiency. Particularly, the hole injection layer and the hole transport layer significantly improve the luminous efficiency.
The organic EL device according to this invention is preferably supported on the substrate. Any substrate may be used as far as it has sufficient mechanical strength, thermal stability and transparency. Glass and transparent plastic film, etc. may be cited as examples.
Anode materials used for the anode of the organic EL device of this invention include metals, metal alloys, electrically conductive compounds and mixtures thereof, which have a work function of more than 4 eV. Metals such as Au and electroconductive transparent materials such as CuI, indium tin oxide (hereinafter referred to as xe2x80x9cITOxe2x80x9d), SnO2 and ZnO may be cited as examples.
Cathode materials used for the cathode of the organic EL device of this invention include metals, metal alloys, electrically conductive compounds and mixtures thereof, which have a work function of less than 4 eV. Calcium, magnesium, lithium, aluminum, magnesium alloy, lithium alloy, aluminum alloy, and mixtures of aluminum/lithium, magnesium/silver and magnesium/indium, etc. may be cited as examples.
In this invention, the light transmittance of at least one electrode is preferably not less than 10% so as to efficiently obtain the light emission from the organic EL device. The sheet resistance as an electrode is preferably not more than several hundred xcexa9/mm. The film thickness depends on the property of electrode materials, but it is usually selected within a range of 10 nm to 1 xcexcm, and preferably 10-400 nm. Such electrodes may be manufactured by a method such as vapor deposition and sputtering wherein a thin film is formed using the above-mentioned electrode material (anode material and cathode material).
The luminescent layer as an essential layer of the organic EL device of this invention preferably comprises the borane derivatives represented by the aforementioned formula (2). However, any luminescent materials other than the borane derivatives of this invention may be used. It is also possible to use the mixture of the borane derivatives of the formula (2) and other luminescent material in order to obtain a light wavelength different from that of the borane derivative, or to enhance the luminous efficiency. Further, there is no problem in using two or more borane derivatives of the formula (2) in combination.
The luminescent materials other than the borane derivatives of the formula (2) may include various known materials such as daylight fluorescent materials mentioned in xe2x80x9cOptical Function Materialsxe2x80x9d, Functional Polymer Material Series, Society of Polymer Science, Japan ed., Kyoritsu Shuppan Co., Ltd. (1991), p. 236, optical whitening agents, laser dyes, organic scintillators, various fluorescence analysis reagents.
Specifically, preferred are polycyclic condensation compounds such as anthracene, phenanthrene, pyrene, chrysene, perylene, coronene, rubrene and quinacridone; oligophenylene compounds such as quarterphenyl; scintillators for the liquid scintillation such as 1,4-bis(2-methylstyryl)benzene, 1,4-bis(4-methylstyryl)benzene, 1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene, 1,4-bis(5-phenyl-2-oxazolyl)benzene, 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene, 1,4-diphenyl-1,3-butadiene, 1,6-diphenyl-1,3,5-hexatriene and 1,1,4,4-tetraphenyl-1,3-butadiene; metal complexes of oxine derivatives disclosed in JP-A 63-264692; coumarin dyes; dicyanomethylene pyran dyes; dicyanomethylene thiopyran dyes; polymethine dyes; oxobenzanthracene dyes; xanthene dyes; carbostyril dyes and perylene dyes; oxazine compounds disclosed in Germany Patent No. 2534713; stilbene derivatives disclosed in the 40th Japan Applied Physics Related Association Lecture Proc., 1146 (1993); spiro compounds disclosed in JP-A 7-278537; and oxadiazoles disclosed in JP-A 4-363891.
The hole injection layer, which is an optional layer of the organic EL device of this invention, can be prepared by using the hole injection material. The hole injection layer may be prepared as a single layer comprising one or more hole injection materials or as multiple hole injection layers comprising various hole injection materials.
The hole transport layer, which is an optional layer of the organic EL device of this invention, can be prepared by using the hole transport material. The hole transport layer may be prepared as a single layer comprising one or more hole transport materials or as multiple hole transport layers comprising various hole transport materials.
The hole injection material and the hole transport material may comprise the borane derivatives of the formula (2), but it is also possible to use any material which has been conventionally used as a charge transport material for an positive hole in a photoconductive material, or any known material which can be used for hole injection layers or hole transport layers of the organic EL devices.
Concrete examples of such known materials include, for example, carbazole derivatives (e.g., N-phenyl carbazole, polyvinyl carbazole, etc.); triarylamine derivatives (e.g., TPD, polymers having an aromatic tertiary amine in its principal chain or its side-chain, 1,1-bis(4-di-p-tolylaminophenyl)cyclohexane, N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-dinaphthyl-4,4xe2x80x2-diaminobiphenyl (hereinafter abbreviated as xe2x80x9cNPDxe2x80x9d), 4,4xe2x80x2,4xe2x80x3-tris{N-(3-methylphenyl)-N-phenylamino}-triphenylamine, compounds disclosed in Journal of the Chemical Society, Chemical Communication, p. 2175 (1996), compounds disclosed in JP-A 57-144558, JP-A 61-62038, JP-A 61-124949, JP-A 61-134354, JP-A 61-134355, JP-A 61-112164, JP-A 4-308688, JP-A 6-312979, JP-A 6-267658, JP-A 7-90256, JP-A 7-97355, JP-A 6-1972, JP-A 7-126226, JP-A 7-126615, JP-A 7-331238, JP-A 8-100172 and JP-A 8-48656, and star-burst amine derivatives described in Advanced Material, Vol. 6, p. 677 (1994), etc.), stilbene derivatives (those disclosed in 72nd CSJ (the Chemical Society of Japan) National Meeting, Lecture Proc. (II), p. 1392, 2PB098, etc.); phthalocyanine derivatives (non-metal, copper phthalocyanine, etc.); and polysilanes.
The electron injection layer, which is an optional layer of the organic EL device of this invention, can be prepared by using the electron injection material. The electron injection layer may be prepared as a single layer comprising one or more electron injection materials or as a multiple electron injection layer comprising various electron injection materials.
The electron transport layer, which is an optional layer of the organic EL device of this invention, can be prepared by using the electron transport material. The electron transport layer may be prepared as a single layer comprising one or more electron transport materials or as a multiple electron transport layer comprising various electron transport materials.
The electron injection material and the electron transport material preferably comprise the borane derivatives of the formula (2), but it is also possible to use any material which has been conventionally used as an electron transfer compound in a photoconductive material, or any known material which can be used for electron injection layers or electron transport layers of the organic EL devices.
Concrete examples of such known materials include, for example, diphenylquinone derivatives (those disclosed in Journal of the Society of Electrophotography of Japan, 30, 3 (1991), etc.), perylene derivatives (those described in J. Apply. Phys., 27, 269 (1988), etc.), oxadiazole derivatives (those disclosed in the above mentioned Lit., Jpn. J. Appl. Phys., 27, L713 (1988), and Appl. Phys. Lett., 55, 1489 (1989), etc.), thiophene derivatives (those disclosed in JP-A 4-212286, etc.), triazole derivatives (those disclosed in Jpn. J. Appl. Phys., 32, L917 (1993), etc.), thiadiazole derivatives (those disclosed in Polymer Preprints, Japan, Vol. 43, No. 3 (1994), (III) Pla007, etc.), metal complexes of oxine derivatives (those disclosed in Technical Report of Institute of Electronics, Information and Communication Engineers, 92 (311), 43 (1992), etc.), polymers of quinoxaline derivatives (those disclosed in Jpn. J. Appl. Phys., 33, L250 (1994), etc.), and phenanthroline derivatives (those disclosed in Polymer Preprints, Japan, Vol. 43, No. 7 (1994), 14J07, etc.)
Hole injection materials, hole transport materials, luminescent materials and electron injection materials, which are usable in the organic EL device of this invention, preferably have a Tg of not less than 80xc2x0 C., more preferably not less than 100xc2x0 C.
Preferable interlayers, which are optional layers of the organic EL device of this invention, are those which can promote the injection of the electron from the cathode, and those which can prevent the positive hole from flowing into the cathode. These are selected according to the compatibility with the material used for the cathode. Lithium fluoride, magnesium fluoride, calcium fluoride, etc. may be cited as concrete examples.
Each layer constituting the organic EL device of this invention may be prepared by forming the material for constituting the layer into a thin film by any known method such as vapor deposition, spin coating and casting.
The film thickness of each layer formed by such a method is not particularly limited, and it can be properly determined depending upon properties of the material used. It is usually selected within the range of 2 nm to 5000 nm.
When the vapor deposition method is used to form the material into a thin film, the depositing conditions may be varied depending on the kind of the borane derivatives, the crystalline structure and the associated structure of the intended molecular built-up film. In general, it is preferably selected within the following ranges: the boat heating temperature of 50 to 400xc2x0 C., vacuum of 10xe2x88x926 to 10xe2x88x923 Pa, deposition rate of 0.01 to 50 nm/sec., substrate temperature of xe2x88x92150 to +300xc2x0 C., and film thickness of 5 nm to 5 xcexcm.
Next, the method of manufacturing the organic EL device, which has the aforementioned structure (1) comprising anode/borane derivative layer/cathode, is explained as an example of the method for producing the organic EL device of this invention.
A thin film comprising an anode material is formed on an adequate substrate by the vapor deposition method so as to be 1 xcexcm or less, preferably 10 to 200 nm, in thickness. Then, a thin film of the borane derivative is formed onto the resulting anode layer to obtain a luminescent layer. A thin film comprising a cathode material is formed onto the luminescent layer by the vapor deposition method so as to be 1 xcexcm or less in thickness, resulting in a cathode layer. The desired organic EL device is thus obtained.
Alternatively, the order of manufacturing the above-mentioned organic EL device can be reversed, namely, the cathode, the luminescent layer and the anode may be produced in order.
When applying a DC voltage to the resultant organic EL device, it may be applied with the anode set to a positive polarity and the cathode set to a negative polarity. If applying a voltage of approximately 2 to 40 V, the light emission can be observed from the transparent or semi-transparent electrode side (anode or cathode, and both).
This organic EL device can emit lights as well when applying an AC voltage. Any waveform of the AC may be applied.
Now, the present invention shall specifically be explained with reference to the following examples, but this invention shall not be limited thereto.
Synthesis of Borane Derivatives